Searching through content which is accessible through web-based forms

ABSTRACT

One embodiment of the present invention provides a system that facilitates searching through content which is accessible though web-based forms. During operation, the system receives a query containing keywords. Next, the system analyzes the query to create a structured query. The system then performs a lookup based on the structured query in a database containing entries describing the web-based forms. Next, the system ranks forms returned by the lookup, and uses the rankings and associated database entries to facilitate a search through content which is accessible through the forms.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. section 119(e) to U.S.Provisional Application Ser. No. 60/669,292, entitled “Deep-Web SearchEngine and Associated Tools,” by the same inventors as the instantapplication, filed on 6 Apr. 2005, the contents of which are hereinincorporated by reference. The subject matter of this application isalso related to the subject matter in a co-pending non-provisionalapplication by the same inventors as the instant application and filedon the same day as the instant application entitled, “FacilitatingSearches through Content which is Accessible through Web-Based Forms,”having U.S. application Ser. No. 11/398,970, and filing date 5 Apr.2006.

BACKGROUND

1. Field of the Invention

The present invention relates to techniques for performing searchesthrough content on web sites. More specifically, the present inventionrelates to a method and an apparatus that facilitates searching throughcontent which is not directly available on web pages, but is insteadaccessible though queries entered into web-based forms.

2. Related Art

Much of the power of the World Wide Web arises from the ability ofsearch engines to rapidly comb through billions of web pages looking forpages associated with keywords of interest. Unfortunately, a largeportion of the data which is available on the web is hidden behindweb-based forms, and is consequently not searchable by traditionalsearch engines.

A user typically accesses this type of data by filling in input fieldsin a web-based form. This causes a corresponding database query to begenerated based on the values contained in the input fields, and thedatabase query is submitted to an underlying database. This query causesdata to be returned, and this data is typically displayed to a user. Forexample, a web-based form for local property tax records can accept anaddress in a set of input fields and can output a corresponding propertytax record for the address. In another example, a web-based form for achain of coffee shops can accept a city name or a postal code in a setof input fields and in response can display the locations of nearbycoffee shops.

Traditional search engines lack the ability to search through this typeof data which is hidden behind web-based forms. Consequently, a largeamount of possibly relevant data cannot be easily accessed throughtraditional search engines.

Hence, what is needed is a method and an apparatus that facilitatesefficiently searching through information which is hidden behindweb-based forms.

SUMMARY

One embodiment of the present invention provides a system thatfacilitates crawling through web-based forms to gather information tofacilitate subsequent searches through content which is accessiblethough the web-based forms. During operation, the system first obtainsweb-based forms to be searched. Note that the system can obtain theseweb-based forms from a number of sources. For example, the system cancrawl through web sites to identify web-based forms, the system canreceive manually provided web-based forms, or the system can findweb-based forms through methods other than crawling. Next, the systemcreates database entries for the identified forms. This involvesobtaining and storing metadata describing the identified forms intodatabase entries and then storing these database entries in a formdatabase to facilitate searches through content which is accessiblethrough the identified forms. Note that this form database can include aweb index and associated documents, which can be used to facilitate websearch queries that return both ordinary documents and documents thatresult from form queries.

In a variation on this embodiment, obtaining the web-based forms to besearched involves manually or automatically filtering out otherweb-based forms, which are not to be searched.

In a variation on this embodiment, the system additionally extractscontent from a given form, and stores the extracted content tofacilitate subsequent searches through the content.

In a further variation, extracting the content from the given forminvolves accessing the given form through a Uniform Resource Locator(URL) which contains a GET-string that extracts the content from thegiven form.

In a further variation, extracting the content from the given forminvolves: generating constants to be inputted into the given form; usingthe constants to fill input fields of the given form; extracting thecontent from associated output fields of the given form; and storing thecontent in the form database to facilitate subsequent queries involvingthe content.

In a further variation, extracting and storing the content from thegiven form involves: obtaining constants associated with a given fieldof the given form from a drop-down menu associated with the given field;and storing the constants, whereby the constants can be subsequentlyused as inputs to the given field or as inputs to similar fields inother forms during subsequent query operations.

In a variation on this embodiment, obtaining metadata about anidentified form involves obtaining information related to the source ofthe identified form. This can involve identifying: a class of thesource; a geographic location most relevant to the source; and/or apage-rank of the source.

In a variation on this embodiment, obtaining metadata about anidentified form involves identifying: a class of the identified form; ageographic location which is most relevant to objects retrieved from theidentified form; fields of the identified form; required input fields orrequired combinations of input fields for the identified form; and/ormappings between fields of the identified form and associated classproperties.

In a variation on this embodiment, a given form generates values foroutput fields by: forming a database query from constants receivedthrough input fields of the given form; sending the database query to adatabase system; receiving a response from the database system; andoutputting data returned in the response through output fields of thegiven form.

One embodiment of the present invention provides a system thatfacilitates searching through content which is accessible thoughweb-based forms. During operation, the system receives a querycontaining keywords. Next, the system analyzes the query to create astructured query. The system then performs a lookup based on thestructured query in a database containing entries describing theweb-based forms. Next, the system ranks forms returned by the lookup,and uses the rankings and associated database entries to facilitate asearch through content which is accessible through the forms.

In a variation on this embodiment, while analyzing the query to createthe structured query, the system first predicts a search-ontology classfor the query based on keywords in the query. The system then constructsthe structured query by mapping keywords in the query to properties ofthe predicted search-ontology class.

In a variation on this embodiment, facilitating the search involvesfacilitating a search through one or more forms of interest, which wereidentified during the ranking process.

In a further variation, facilitating the search through the one or moreforms of interest involves presenting a highly-ranked form to a userthrough a “one-box” displayed prominently within a user interface.

In a further variation, while facilitating the search through the one ormore forms of interest, the system first presents a user withquery-through links to the one or more forms of interest. The systemthen allows the user to click on a query-though link which automaticallycauses a corresponding query to be submitted to an associated form ofinterest.

In a further variation, while presenting the user with a query-throughlink to a form of interest, the system first maps keywords from thequery to input fields in the form of interest. Next, the systemconstructs a query-though link based on the mappings, which contains aninvocation string to be submitted to the form of interest. The systemthen presents the query-through link to the user.

In a further variation, facilitating the search through the contentinvolves searching through a local database containing content which waspreviously extracted from the forms during a preceding web-crawlingprocess.

In a variation on this embodiment, ranking a form involves considering:an approximate page-rank score reflecting the number of incoming linksto a web page associated with the form; a keyword score reflecting therelevance of text associated with a web page associated with the form;an ontology score which captures the relevance of a search ontologyclass selected for the query to a web page associated with the form; aform score which captures the ability of the form to answer the query;and/or a location score which captures the distance from the mostrelevant location for a web page associated with the form from locationsdetected in the query.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a form engine which facilitates the process ofsearching through web-based forms in accordance with an embodiment ofthe present invention.

FIG. 2 illustrates the structure of a form engine in accordance with anembodiment of the present invention.

FIG. 3 illustrates entries contained in a form database in accordancewith an embodiment of the present invention.

FIG. 4 presents a flow chart illustrating the process of crawlingthrough web pages to gather information related to web-based forms inaccordance with an embodiment of the present invention.

FIG. 5 presents a flow chart illustrating the process of retrievingpages from a form in accordance with an embodiment of the presentinvention.

FIG. 6 presents a flow chart illustrating the process of searchingthrough content which is accessible through web-based forms inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present invention. Thus, the present invention is notlimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the claims.

The data structures and code described in this detailed description aretypically stored on a computer-readable storage medium, which may be anydevice or medium that can store code and/or data for use by a computersystem. This includes, but is not limited to, magnetic and opticalstorage devices such as disk drives, magnetic tape, CDs (compact discs),DVDs (digital versatile discs or digital video discs), or any devicecapable of storing data usable by a computer system.

System

FIG. 1 illustrates a form engine 106 which facilitates searching throughweb-based forms in accordance with an embodiment of the presentinvention. Form engine 106 can generally exist on any computing devicewhich is accessible through network 110. This computing device caninclude any type of computing device, including, but not limited to, acomputing device based on a microprocessor, a mainframe computer, adigital signal processor, a portable computing device, a personalorganizer, a device controller, and a computational engine within anappliance. Network 110 can generally include any type of wired orwireless communication channel capable of coupling together computingnodes. This includes, but is not limited to, a local area network, awide area network, or a combination of networks. In one embodiment ofthe present invention, network 110 includes the Internet.

During a web-crawling process, form engine 106 accesses a number offorms 121-123 which are hosted on servers located throughout network110. These forms 121-123 can be used to access to data within underlyingdatabases 131-133. During this web-crawling process, form engine 106first obtains web-based forms of interest, and then createscorresponding database entries for the identified forms in an associatedform database 107. Note that the system can obtain these web-based formsfrom a number of sources. For example, the system can crawl through websites to identify web-based forms, the system can receive manuallyprovided web-based forms, or the system can find web-based forms throughmethods other than crawling.

During subsequent searching operations, form database 107 is used byform engine 106 to facilitate searches through content which isaccessible through the web-based forms which are cataloged within formdatabase 107. More specifically, a user 102 operating a client 104 cansend a query 108 containing keywords to form engine 106. In response toquery 108, form engine 106 uses information within form database 107 toperform a search through content which is accessible through forms121-123. Note that form database 107 can include a web index andassociated documents, which can be used to facilitate web search queriesthat return both ordinary documents and documents that were obtainedfrom form queries.

Form Engine

FIG. 2 presents an overview of form engine 106 (which is also referredto as a “deep-web search query engine”) in accordance with an embodimentof the present invention. As illustrated in FIG. 2, form engine 106includes a set of tools that facilitate constructing a search engine forthe “deep web.” The deep web refers to the part of the web that hidesbehind forms and is therefore not accessible to traditional searchengines. With these tools, both a general-purpose search engine, anddomain-specific engines that focus on certain topics, may beconstructed. As illustrated in FIG. 2, the tools include: a query engine202; a web-form database 204; and a web crawler 206 (which includes formanalyzer). During system operation, web crawler 206 first obtainsweb-based forms of interest, and stores corresponding form-relatedinformation for the web-based forms of interest in web-form database204. Next, query engine 202 accesses this form-related information fromweb-form database 204 to facilitate subsequent searching operationsthrough content which is accessible through the web-based forms. Theseand other aspects of the present invention are described in more detailbelow.

The Database Schema

In one embodiment of the present invention, the database describes websources in terms of an ontology of classes and properties, which isreferred to as the “search ontology” (SO). The classes and propertiesare referred to as “SO-classes” and “SO-properties,” respectively. Invarious embodiments, the SO-classes form a hierarchy (not necessarily atree, but a directed acyclic graph). Moreover, the SO-properties havedomains (the classes in the ontology they refer to), and ranges (eitherdata types or other classes in the ontology). In various embodiments,any knowledge-base editing tool can be used to create the ontology. Invarious embodiments, the SO is exported into a Web Ontology Language(OWL) file.

In various embodiments, the database has a distinct data “source” oreach web page (identified by its URL) is a data source. (Note that theterms “web page,” “data source” and “web source” are usedinterchangeably in this document.) The database captures at least someof the following aspects of each source:

-   -   1. the class of the source (e.g., a portal, university,        newspaper);    -   2. the geographic location most relevant to the source (when        applicable), e.g. the city of Seattle in Washington state for        the Seattle Times; and    -   3. the page rank of the source.

For each form in the source the following information can be captured.

-   -   1. Fields in the form—For each field the information recorded        can include its parameter name (used to invoke some server-side        script), the human-readable or visible text for that field,        field types (text, select box, radio button, or checkbox), and        exemplary values for the field (e.g., the options in a select        box).    -   2. The class of the form—This information specifies the types of        objects that can be obtained by querying the form. For example,        books, hotels, restaurants. Note that a source can have several        forms on it, and they can relate to different classes of objects        (e.g., newspapers often have forms for looking for houses, jobs        and cars for sale).    -   3. Geographic location—This information specifies a geographic        location which is specific to the objects retrieved using the        form.    -   4. Required fields—These are field which are required to submit        the form. In some cases, there are multiple combinations of        fields that can satisfy the requirements.    -   5. Output properties—This specifies the type of information we        will obtain from answers to a successful form submission. These        are described as the SO-properties we are likely to find in the        answers.    -   6. Schema mapping—This is the mapping between the fields in the        form and the SO-properties. Note that in some cases, these        mappings may be complex. For example, it is common for a field        to ask for either the ZIP code or the city and state. This        mapping can involve multiple SO-properties, but our database        records the exact combinations of SO-properties that can be        filled in the field.    -   7. Additional keywords—These are additional keywords that        describe the web form.        Creating Content for Source Database

In one embodiment of the present invention, a set of candidate websources is collected and processed as described below to predict thedatabase attributes associated with each source. The result of thisprocessing can be shown to a human annotator who can certify thedatabase contents and can change them if necessary. Note that it doesnot matter where the candidate sources are obtained from. A special setof crawlers that discover content which is especially appropriate forthe engine is described below.

Web Source Preparation

In one embodiment of the present invention, the first step in processinga web source is to locate the forms in the source and to extract thetext corresponding to the fields in the form.

Web Page Classification

In one embodiment of the present invention, the web source issubsequently classified into the ontology classes. Note that the classof the source is being classified, not the objects found in a form inthe source. In various embodiments, a TF/IDF text classifier isemployed. In various embodiments, each web page is represented as a wordvector with each word having its weight set as the product of termfrequency (number of occurrence on the page) and its inverse documentfrequency (1/log(1+number of pages with the word)). The weights are allnormalized such that the word vector is of unit length. As trainingdata, web pages that have already been labeled with SO-classes are used.In the training phase, given these labeled web pages, the mean wordvector mv(c_(i)) is computed for each search class c_(i). To predict theSO-class for any new web page, the cosine measure between its wordvector and the mean vector for each of the search classes can becomputed. In various embodiments, the search classes with the threehighest values for the cosine measure are chosen as candidate searchclass matches. Note that the contents of a web page can first bepre-processed to remove any stop words and to stem all possible words.

Web Form Classification

Next, in various embodiments the forms on the page are classified intothe classes in the ontology. This classification attempts to predictwhich kinds of objects would be found in the database queried by theform. Note that this is quite different than classifying the formitself, and that the context of the page may or may not provide goodpredictive power about the classification. For example, on a recipesite, the words on the site are typically very indicative of the contentof the database. However, on a newspaper site, we may see several forms(for real-estate, used cars, job ads) and the words on the page mayprovide no clue as to the content of the corresponding databases.

In various embodiments, the same idea of a TF/IDF classifier isemployed. Two word vectors are computed for each web form: a word vectorfor the entire web page (same as for the web page classifier), and aword vector for the form that includes just the words that appear in theform and just before and after the form. Furthermore, two separateclassifiers are trained using the labeled training data. Note that thistraining in done for both the classifiers on the labels of the form, andnot the page. Moreover, note that these labels are different from thoseused by the web page classifier. When classifying new forms, bothtrained classifiers are applied on the form contents. Their results arecombined based on the number of forms on the same web page. If there area number of forms on the page, then the prediction made by the page textclassifier is given a lower weight:sim(f,c _(i))=pf×sim _(page)(f,c _(i))+(1−pf)×sim _(form)(f,c _(i))where sim(f,c_(i)) is the predicted similarity of the form f and theSO-class c_(i), and where the page factor pf=0.3+0.6/(num forms onpage).

Predicting Required Fields and Output Fields

In various embodiments, required input fields and output fields arepredicted based on past experience. For each class in the ontology, welook at previously annotated sites and find which fields have beenmarked as required or output. In various embodiments, there may beseveral clusters of possible output fields, and these clusters may bemined, and displayed to the user so that the user may make a selection.

Schema Matching

Next, in various embodiments, a mapping between the fields in the formand the SO-properties of the SO-classes that the form had been mapped tois predicted. This can involve employing an LSD-like multi-strategyapproach for predicting field to property mappings. (For moreinformation on LSD, see A. Doan, P. Domingos, and A. Levy, “ReconcilingSchemas of Disparate Data Sources: A Machine-Learning Approach,” SIGMOD2001, pp. 509-520.) In doing so, each SO-class can be treated as aseparate field-matching problem: the mediated schema has theSO-properties of that class. Moreover, each web form is a source schema,and example mappings are provided where the fields of the web form arematched to properties of the search class. This labeled training data isused to train a variety of base classifiers and also a meta-classifierthat combines the predictions of the different base classifiers.

The different base classifiers we can use include: (a) an internal namematcher that uses edit distance to compare parameter names of thefields, (b) a visible text matcher that uses TFIDF to compare the textthat can be easily associated with each visible field, (c) an instancematcher that uses TFIDF to compare the text in the different options fora field value, e.g. for a select box or radio button.

In various embodiments, to implement the meta-classifier, themeta-classifier library in the Weka™ toolkit, which is similar to thetechnique used in LSD, can be used to learn a separate combinationhypothesis for each field. Moreover, the trained base andmeta-classifiers can be used to compute similarities between each webform fields and search class properties.

In various embodiments, a constraint-solving mechanism is used to outputthe specific matches. The match selection can be modeled as a costminimization process, wherein the cost of selecting a particular set ofmatches is dependent on the similarities estimated between the elementsin the chosen matches. In addition, desirable properties of the mappingscan be encoded as costs and included as part of the minimizationprocess, e.g. a penalty cost of mapping more than one field to the sameSO-property.

This cost minimization may be performed using a randomized technique.For example, the process can start with a random assignment. Then, oneelement (web form field or SO-property) can be considered at a time andthe system can try to match it with the best possible candidate elementin the other schema (given the mappings for the rest of the elements inweb form and SO-class) so as to minimize/reduce the cost of the mapping.Note that the definition of “best possible candidate” may beimplementation dependent. This process continues until the mappingconverges or until a fixed number of iterations occur.

In summary, given a new web page, a web-page classifier can used topredict the SO-class for the source. Next, a web-form classifier can beused to identify the top candidate SO-classes for each web form on theweb page. Then, for each web form and given candidate SO-class, theform-field-to-SO-property matcher can be invoked to compute similaritiesbetween the fields on the web form and the properties of the searchclass. A constraint satisfaction module can then be invoked to pick theparticular field-to-SO-property matches.

Location Prediction

In various embodiments of the present invention, for each web page, themost likely country or state, and within it the most likely city, arealso predicted. In various embodiments, during the location analysis, atwo-level hierarchy of locations is considered: the first level includesall the countries of the world (except the U.S.) and the states in theU.S., and the second level includes cities. In various embodiments, itis assumed that city names are unique within each country or U.S. state.For ease of understanding, in the discussion below, sometimes onlystates are referred to, but the same holds true for countries as well,unless otherwise mentioned.

In various embodiments, the location prediction may be done as follows.First, for each country or U.S. state, its location score is computed:

${L\left( s_{i} \right)} = {\sum\limits_{w_{j}}{{L_{s}\left( {w_{j},s_{i}} \right)}.}}$wherein each word w_(j) in the web page text contributes L_(s)(w_(j),s_(i)), a measure of the likelihood that it represents a location in thecountry or state s_(i). The most likely state is the one with thehighest location score, provided the score is greater than a thresholdt_(L). No state is predicted if none of the scores are greater thant_(L).

Each score L_(s)(w_(j), s_(i)) contributed by each word is computed asone of the following:

-   -   (a) C_(state)×idf(w_(j)) if w_(j) is the name of the state (or        its abbreviation), wherein idf(w) is the inverse document        frequency of the word w (defined below);    -   (b) C_(city)×idf(w_(j))×popl(w_(j), s_(i)) if w_(j) is the name        of a city within the state, wherein popl(w_(j), s_(i)) depends        on the population of the city named w_(j) in the state s_(i);        and    -   (b) C_(zip)×idf(w_(j))×popl(w_(j), s_(i)) if w_(j) is the zip of        a city within the state, wherein the population score is that of        the corresponding city.

In the above, the population score popl(w, s) can be defined as follows:

${{popl}\left( {w_{j},s_{i}} \right)} = \left\{ \begin{matrix}{1 + {\log\left( \frac{\max\left( {{{population}\left( {w_{j},s_{i}} \right)},10000} \right.}{10000} \right)}} & {{{if}\mspace{14mu} w_{j}\mspace{14mu}{is}\mspace{14mu} a\mspace{14mu}{city}},} \\2 & {otherwise}\end{matrix} \right.$Moreover, the inverse document frequency (IDF) of a word can be definedas follows:

${{{idf}(w)} = {1.5 \times \frac{\log\mspace{11mu} 5}{\log\left( {5 + {{count}(w)}} \right)}}},$where count(w) is the number of web pages in our collection that containthe word w. Thus, the IDF score can vary from 1.5 to 0 depending on thefrequency of the word.

Note that each word can correspond to multiple locations, e.g., citiesin different states and countries. In this case, such a word contributesto the location score of each of the states or countries.

In various embodiments, the case of state and city names consisting ofmultiple words is also handled. In doing so, the web page text is firstpre-processed to identify all such multi-word location names which arethen treated as single words.

In alternate embodiments, lexical or grammatical analysis of the text onthe web page may also be performed.

In various embodiments, once the most likely U.S. state or country hasbeen recognized, the location scores for each city within it is computedby using the criteria (b) and (c) in the above list. In variousembodiments, a city is predicted if its score is more than 0.3 of thestate/country location score.

For example, for the University of Washington Computer Science &Engineering homepage, the predicted locations are WASHINGTON State andSEATTLE, while for the Yahoo main page no locations are predicted.

Site Crawler

Web sites typically support query interfaces on multiple web pages whichenable access to data in different sources. For example, the New YorkTimes has web forms for the weather and classifieds in the New Yorkregion, stock tickers for the different stock exchanges, etc. The sitecrawler explores such a web site (a domain like nytimes.com for the NewYork Times) to discover all such available web forms.

Like a typical crawler, the site crawler pursues hyperlinks recursivelystarting from a seed page (e.g., the main page of the web site). Inaddition, it can perform two operations for discovering web forms.

-   -   1. It filters web forms. More specifically, for each new web        page discovered by the crawler, it determines whether the web        forms on the page, if any, are interesting and worth recording        (e.g., email subscription forms are not very interesting and may        be ignored).    -   2. It reconciles duplicate web forms. Very often the same web        form appears on different web pages in the same web site, and        the duplicate web forms are detected to prevent multiple        recordings of the same source.

In various embodiments, the filtering of web forms may be done in asemi-automatic fashion. Classifiers are employed to predict the utilityof each form (i.e., should the form be considered or ignored). Theseclassifiers are trained from manually-supplied training data. Each webform has a utility score that is the score reported by the classifier.The web pages on each web site can be ranked in decreasing order of thescores of their forms. A user may be requested to scan this list toidentify the most useful ones while the rest are ignored.

Two web forms are considered to be identical if they invoke the samemethod and use exactly the same parameter values. During thereconciliation process, the forms on each page are compared againstalready extracted forms and are eliminated if an identical form alreadyexists. As part of the reconciliation process, the crawler alsodetermines which of the multiple occurrences of a web form have to beretained as the principal instance. For example, weather reports areavailable both from the “cnn.com” and “money.cnn.com sites,” but“money.cnn.com” might be the more suitable one. In various embodiments,simple heuristics are used to make this selection: (a) larger domainnames (with the same suffix, e.g., money.cnn.com as opposed to cnn.com)typically refer to more-specific web sites and hence are preferred,while (b) smaller path names refer to more authoritative pages and arehence preferred.

Web forms on a web page can often refer to methods in different domains(e.g., the auto sales form on New York Times is redirected to a methodon cars.com). These references indicate the importance of the referencedsource and are recorded separately for the ranking process. In variousembodiments, they are not reconciled since they typically have differentparameter values (with information specific to the referring web site).

Querying and Ranking

Query Analyzer

The query analyzer can be adapted to consider keyword queries from auser and to predict the SO-class in the ontology that is most relevantto the query. During this process, a structured query is alsoconstructed from the user query.

In various embodiments, three types of prediction can be used to predictthe most likely search class for each query: (1) word-based prediction;(2) property-based prediction; and (3) feedback-based prediction. Thesetypes of prediction are described in more detail below.

Word-Based Prediction

Words are often strongly correlated with specific SO-classes and thiscorrelation can be used a basis for class prediction. In variousembodiments, a naïve-Bayes-like scheme, augmented with featureselection, can be employed. The predicted class is the one that is mostlikely to generate the words in the search query. For example, if theuser query is w₁w₂ . . . w_(n), then

$C = {{\arg\mspace{11mu}{\max_{C_{i}}\mspace{11mu}{P\left( {w_{1}\mspace{11mu}\ldots\mspace{11mu} w_{n}} \middle| C_{i} \right)}}} = {\arg\mspace{11mu}{\max_{C_{i}}{\prod\limits_{w_{j}}{{P\left( w_{j} \middle| C_{i} \right)}.}}}}}$The probability of each class, i.e. P(w₁w₂ . . . w_(n)|C_(i)), isobtained by normalizing the scores computed in the above expression suchthat they sum to 1. Described below is how the marginal probability canbe estimated for each word and feature selection in accordance with anembodiment of the present invention.

Marginal Probability Estimation—In various embodiments, the marginalprobability of each word is given by the expression:

${P\left( w_{j} \middle| C_{i} \right)} = \frac{{K\frac{1}{W}} + {\sum\limits_{d_{k} \in D_{i}}{D\left( {w_{j},d_{k}} \right)}}}{K + {D_{i}}}$where D(w_(j), d_(k)) is the weight of word w_(j) in the document d_(k)(each document has a total weight of 1, and the weight of each word isproportional to the number of occurrences of this word in the document).Moreover, D_(i) is the set of documents that have been labeled withclass C_(i), and K is the smoothing constant which is greater than 0.The smoothing ensures that in the absence of any training data themarginal probability distribution is uniform (1/|W|).

Feature Selection—Since a small amount of training data is employed, inorder to avoid over-fitting, in various embodiments, only those wordsthat are discriminative enough are used. In various embodiments, theability of a word to discriminate between SO-classes can be measured byits entropy:

${H\left( w_{j} \right)} = {- {\sum\limits_{C_{i}}{{P\left( w_{j} \middle| C_{i} \right)}\log\mspace{11mu}{P\left( w_{j} \middle| C_{i} \right)}}}}$The marginal probabilities P(w_(j)|C_(i)) are normalized so that theysum to 1. All the words are sorted by their entropies and only the onesthat are greater than a particular threshold are included. Furthermore,in various embodiments, (a) only words that have appeared in at least Ndifferent pages in total (typically 10-15), are considered, (b) only thetop 10 classes for each word while computing the entropy are considered,and (c) probabilities for the non-top 10 classes are set to be equal tothat of the 10th search class. Note that the above definition is notexactly the technical definition of entropy since entropy is betterdefined when computed on P(C_(i)|w_(j)). In various embodiments, featureselection may be performed via Mutual Information and the FisherDiscriminant.Property-Based Prediction

In various embodiments, property recognizers are employed to identifyinteresting constants in user queries. SO-classes can be predicted basedon the properties recognized. For example, the most likely class may bethe one that is most likely to generate the recognized property valuesin the user query (e.g., Acura is the name of a car make and Integra isthe name of a car model, and hence the query “used Acura Integra” ismost likely referring to Cars). The following expression is used todetermine the most likely class:

$C = {\underset{C_{i}}{\arg\mspace{11mu}\max}\mspace{14mu}{{{sigmoid}\left( {\sum\limits_{V_{k} \in {PS}}{\alpha_{k} \times {\beta\left( {V_{k},C_{i}} \right)} \times {\gamma\left( {w_{j} \in V_{k}} \right)}}} \right)}.}}$where PS is the set of all property recognizers, V_(k) is the k-threcognizer, β is a indicator function that is equal to 1 if therecognizer V_(k) recognizes a property of the class C_(i) (and 0otherwise), and α_(k) is the weight or relevance of V_(k). In variousembodiments, each recognizer is trained to recognize examples of aparticular set of search class properties and estimates a confidencescore γ that a word (or sequence of words) is an instance of the trainedproperty. The score for each class is obtained by normalizing theprobabilities for the various search classes to sum to one.

In various embodiments, one or more of the following recognizers can beemployed:

-   -   1. a search-class recognizer which recognizes a word or a        sequence of words representing the name of a class, a part of        the name of the class or a synonym (synonyms are looked up from        a pre-defined list of words associated with each class);    -   2. a property-name recognizer which recognizes a word        representing the name of some property in the ontology;    -   3. a first-and-last-name recognizer which recognizes a common        last name or first name (the score in this case is a measure of        the frequency of the name as per the U.S. Census);    -   4. a location recognizer which recognizes the word or sequence        of words representing a location name, i.e., city, state, or        country name, or a valid U.S. ZIP code.    -   5. a generic-property recognizer which recognizes is the word        representing a known example of a property, i.e., is there a        known mapping from some web form field to the property by which        it can be reasoned that the word is an example of the property        (For example, “Acura” is a car make, since it appears as one of        the options in a select box for car makes in a used car search        web form. This recognizer can reuse the property mappings        predicted by the schema matcher); or    -   6. a year recognizer which recognizes a year between 1900 and        2010.

The recognizer weights are set such that multiple properties may berecognized for a search class to be successfully detected. Many of therecognizers return confidence scores (γ) that are proportional to theIDF score (defined earlier). This enables words that occur rarely to bea unique representation of one class as opposed to others that occurfrequently.

Feedback-Based Prediction

In various embodiments, the first 20 hits from just a keyword query areconsidered. From this, the number of web forms that have been labeled(either manually or automatically) to each SO-class is estimated. If oneparticular class dominates, then that is likely the class most relevantto the user's query. In various embodiments, a SO-class is considered todominate if it is the class with the most number of forms and theseforms account for more than 40% of the top 20 hits. The score for theclass is ½ that of the fraction of the number of hits in the top 20. Invarious embodiments, the probability computed using each of the abovecriteria is combined using the logical-OR operation to determine thefinal search class probability, i.e. p=1−(1−p₁)(1−p₂)(1−p₃).

Location Detection

Given a sentence or a phrase, each word in it can potentially be thename of a location. There can also be multiple locations that have thesame name, e.g. Washington. Accordingly, this module is adapted toidentify the words in a phrase that most likely are the name of somelocation and the most likely single location referred to by that name.In various embodiments, a probabilistic labeling scheme is employed.

Suppose the word w is the name of some location (city, state, orcountry). In general, there can be more than one geographic locationwith that name (e.g., there are many cities in the U.S. with the nameParis, though the most famous one is the one in France). The situationis formulated with letting L_(w) be the candidate locations for a wordw. L_(w) includes the null location to indicate that w while being thename of a location does not refer to any real location (e.g., the wordshome and page in the phrase “home page” do not refer to any locationthough there do exist towns in the U.S. named home and page). Theprobability P(w, l_(i)) that the word w refers to the candidate locationl_(i) in L_(w) is estimated. The probabilities are initialized to be allequal to 1/L_(w). In various embodiments, the probabilities areiteratively re-estimated as below:

${P\left( {{l(w)} = l_{i}} \right)} = {\frac{1}{Z}{\mathbb{e}}^{\sum\limits_{F_{j} \in \Gamma}{k_{j}{({{F_{j}{(l_{i})}} - a_{j}})}}}}$where Γ is a set of features, F_(j)(l_(i)) is the value of the j-thfeature when w refers to the location l_(i), k_(j) is the weight of thefeature, a_(j) is a base offset of the feature, and Z is a normalizationconstant such that

$\left\lbrack {\sum\limits_{i}{P\left( {{l(w)} = l_{i}} \right)}} \right\rbrack = 1.$

The features used are similar to those used for the location prediction.

-   -   1. Population of the location:        -   popl(l_(i))=1+log(max(population(l_(i)),10000)/10000) if            l_(i) is a city; and popl(l_(i))=2 otherwise.    -   2. Inverse document frequency of the word:        -   idf(w)=1.5×log(5)/(log(5+count(w))).    -   3. Co-located candidate locations: If l_(i), one of the        candidate locations for the word w, is a city or state in the        U.S., then

${{{statescore}\left( l_{i} \right)} = {\sum\limits_{w_{j} \neq w}\left\lbrack {\sum\limits_{l_{j} \in {L{(w_{j})}}}{{P\left( {{l\left( w_{j} \right)} = l_{i}} \right)} \times \left( {{{state}\left( l_{j} \right)} = {{state}\left( l_{i} \right)}} \right)}} \right\rbrack}},{else}$${{statescore}\left( l_{i} \right)} = {\sum\limits_{w_{j} \neq w}{\left\lbrack {\sum\limits_{l_{j} \in {L{(w_{j})}}}{{P\left( {{l\left( w_{j} \right)} = l_{i}} \right)} \times \left( {{{country}\left( l_{j} \right)} = {{country}\left( l_{i} \right)}} \right)}} \right\rbrack.}}$

In various embodiments, the probabilities of all words with candidatelocations is iteratively re-estimated until either there is convergence(all words have a candidate location with probability more than 0.5), ora maximum number of iterations are performed. For each word theacceptable candidate locations are ones that have a higher probabilitythan the null location. If the null location has the highest probabilitythen no locations are detected for that word. This labeling process isable to effectively remove locations that have common place names (e.g.,Home Page) and can easily disambiguate locations in the presence ofadditional information (e.g., 98105 Redmond is identified as Seattle,Wash. and Redmond, Wash.). As with the location prediction, there can bea pre-processing step where potential multi-word locations areidentified and then treated as single words for the rest of theanalysis.

Query Description Construction

In various embodiments, once an SO-class has been predicted for a userquery, a structured query is constructed by mapping the individual wordsin the query to properties of the chosen search class. As part of theproperty-based class prediction described earlier, each Recognizercreates a RecognizerResult object. This object contains a number ofRecognizerInfo objects. Each Recognizerinfo object records that therecognizer has identified a particular word (or a sequence of words) inthe query with some confidence to be an example value of a particularSO-property (or a set of properties). Using this information, the querydescription module tries to match each word in the user query to themost likely search class property. In various embodiments, this can bedone using a greedy algorithm. If the name of a search class propertyoccurs in the query, it is identified as a requested output property,i.e. the property must be part of the result of a form submission. Theother words in the user query can be mapped to the SO-property with thehighest confidence score. If a word is not recognized in anyRecognizerInfo object, then it can be left as-is and not forced to anyproperty. A QueryDescription object is then constructed for each searchclass such that its QueriedProperties identify the required outputproperties and ConstrainedProperties identify properties of the searchclass that have some words in the user query mapped to them. Forexample, “Telephone David Ko 98102” results in the structured queryPerson{Telephone=?, FirstName=David, LastName=Ko, ZipCode=98102}.

Ranking

Ranking Criteria

In various embodiments, the search results in response to any searchquery are ranked based on one or more of the following criteria:

An approximate page rank score which captures the importance of aparticular page. This can be estimated as the logarithm of the number ofincoming links to that page.

Keyword scores which capture the IR-like score that computes therelevance of the text on web page to the user's query. There are threecomponents to this: the page-text-score determined from the text on theweb page; the anchor-score determined from text around the top 10incoming links; and the title-score determined from title of the webpages. These scores can be reported directly from the values computed bya library that is used to index the web pages.

Ontology scores capture the relevance of the SO-classes predicted forthe user queried to those of the web pages returned. Given a particularSO-class selected from a user's query, the ontology score has twocomponents: (1) the query-match-score is the probability with which theparticular class was selected (this is not dependent on the content ofthe returned web pages and is the result of the class predictiondescribed earlier); and the ontology-match-score is the highestprobability with which a form on a particular page is classified to thatsearch class.

A form score captures the ability of a form to answer a user's query.The query-analysis module determines for each user query the propertiesthat can be input to any form for a particular SO-class and also theproperties that are expected as output. With this information, a formscore can be computed for each web page, which measures the bestcompatibility of forms of a page to the user query. The form scorecompares this description of the query with the descriptions of thevarious forms, and is computed for each page using the formula

${{{FS}(p)} = {\max\limits_{f \in p}{{FS}(f)}}},$where f is a form that is on page p and

${{FS}(f)} = {\frac{{I_{f}\bigcap Q_{I}}}{{I_{f}\bigcup Q_{I}}} \cdot \frac{O_{f}}{Q_{O}}}$where I_(f) and O_(f) are the input and output properties (i.e., fieldsand results) of a form f, and Q_(I) and Q_(O) are the input and outputproperties extracted from the user query. The first term is the JaccardCoefficient and measures if the values in the user query are sufficientfor invoking a particular form. The second term measures the ability ofa form to produce the outputs required by the user.

A location score captures the distance of the most-relevant location fora web page from locations detected in the user query. The locations fora page can be either manually tagged or the result of automaticprediction. The locations for a query are the automatically detectedones. If both are cities, the location score of a page p within 50 milesof the query location can be given by 1−distance/50. If one of them is acity and the other a state, then a score of 0.5 is assigned if the citylies within the state. In all other cases, a score of 0 is used.

Ranking Combination

In various embodiments, the different score components are combinedusing a linear combination. The weights used in the combination aredependent in part on the query analysis. They are assigned defaultvalues, but (a) when an SO-class is predicted, the weight of theontology match score is increased, and (b) when a location is detected,the weight of the location score is increased.

Automatic Form Invocation (Query Through)

Before a web form can be invoked on behalf of a user, the words in auser query have to be mapped to the correct fields of the web form. Thecorrect method invocation string has to then be determined before theform is submitted. In various embodiments, this can achieved through twooperations: (1) mapping words to field values, and (2) constructing theinvocation string. These two operations are described below.

Mapping Words to Field Values

The result of the query analysis is a query description that includes amapping from the properties of a class to words in the user query. Thesource description for each web form already includes a mapping from thefields of the web form to the properties of the search class. These twosets of mappings are composed so as to associate words with fields. Thisgenerally suffices for text input fields. However, for select boxes,radio buttons, and check boxes, the words for each field have to be thenused to pick the correct internal values for the corresponding input.For example, the word “Washington,” which is one of the options in theselect box might correspond to an internal value 50 (or anything else)that has to be used as the parameter value before invoking the methodfor the form. The mapping from select box values to internal values canbe stored as part of the web form description and can be used to pickthe correct internal values for method invocation. However the words inthe query might not correspond exactly to an option in the select box.In general, we pick the select box option that is the leastedit-distance from the query words. For special data types such as statenames, short forms for state names are used to determine the correctinternal values.

Constructing the Invocation String

Many web sites often use Javascript to modify the method invocationstring before form submission. This is done to prevent each crawling oftheir web forms. These web forms cannot be automatically invoked easily.In various embodiments, to get around this impediment, a Javascriptemulation engine is used. In one implementation, a simple browser clientis invoked, which in turn invokes a JavaScript engine. As part of thedescription of any web form, Javascript fragments on a web page are alsorecorded. Before invoking a web form, the script on the emulation engineis executed to get the modified invocation string if any. The parameters(and their mapped words or internal values) are then concatenated to theinvocation string along with the values for any hidden inputs.

Once the invocation string is completely constructed, it can be used tosubmit the form automatically on behalf of the user. In variousembodiments, the mapping for fields to words and internal values is doneas part of the query processing and result ranking, but the Javascriptemulation is done on the web server on when the user clicks on aparticular result hyperlink. Hence, clicks from the search results pageare directed to the web server, which then redirects it with thecompleted invocation string to the correct target web site. In variousembodiments, this can also be done on the client side.

Process Summaries

Crawling Process

FIG. 4 presents a flow chart illustrating the process of crawlingthrough web pages to gather information related to web-based forms inaccordance with an embodiment of the present invention. The systemstarts by obtaining web-based forms to be searched (step 402). Asmentioned above, the system can obtain these web-based forms from anumber of sources. For example, the system can crawl through web sitesto identify web-based forms, the system can receive manually providedweb-based forms, or the system can find web-based forms through methodsother than crawling. During this form-obtaining process, the system canfacilitate a filtering operation to manually or automatically filter outforms that are not to be searched. This filtering process can be basedon some type of pre-specified criteria.

Next, the system creates database entries for the identified forms (step404). The system then stores the database entries in a form database tofacilitate subsequent searching operations (step 406). Note that thisform database can include a web index and associated documents, whichcan be used to facilitate web search queries that return both ordinarydocuments and documents that result from form queries.

In some cases, the system can also retrieve pages from a given form bysubmitting queries to it (step 408). (This process is described in moredetail below with reference to FIG. 5.) Next, the system stores theretrieved pages into a web index (or into some other type of database)along with other web pages to facilitate searches through the retrievedpages (step 410).

Retrieving Pages From a Form

FIG. 5 presents a flow chart illustrating the process of retrievingpages from a given form in accordance with an embodiment of the presentinvention. During this process, the system uses information stored forthe given form in the form database to generate constants to be inputtedinto specific input fields in the given form (step 502). Next, thesystem uses the constants to fill input fields in the given form (step504). This causes the form to produce corresponding outputs which thesystem stores in a web index (step 506).

Note that extracting the content from the form can involve accessing thegiven form through a Uniform Resource Locator (URL) which contains aGET-string that extracts the content from the given form.

Also note that the process of generating constants for a given field ina given form can involve obtaining constants from a drop-down menuassociated with the given field, and then storing the constants. Thisallows the constants to be subsequently used as inputs to the givenfield or as inputs to similar fields in other forms during subsequentquery operations.

Searching Process

FIG. 6 presents a flow chart illustrating the process of searchingthrough web-based forms in accordance with an embodiment of the presentinvention. The process starts when the system receives a querycontaining keywords (step 602). Next, the system predicts asearch-ontology class for the query based on the keywords (step 604).The system then constructs a structured query from the keywords bymapping keywords to properties of the predicted search-ontology class(step 606).

Next, the system performs a lookup based on the structured query in theform database to identify forms of interest (step 608) and ranks theseforms (step 610).

The system then presents the user with query-through links to the rankedforms of interest (step 612), and allows the user to click on a specificquery-through link to submit a query to the associated form of interest(step 614). This query will hopefully return the content of interest.

If the lookup in the database in step 608 returns a form containingcontent that has been pre-extracted during the crawling process, thesystem can optionally search through the pre-extracted content insteadof having to query the form to obtain the content (step 616). Note thatthis pre-extracted content can be stored in indexed form, like a normalweb page, to facilitate this type of searching operation.

Conclusion

The above described engine and tools provide, but are not limited to,the following innovations.

Database of source descriptions—A database that describes the variousaspects of the data sources is provided to facilitate a deep-web search.This database describes the objects accessed by the form on the websource. The database also identifies classes of objects in the domain.These classes belong to a so called Search Ontology that is used toorganize the classes into an inheritance hierarchy. The database alsoidentifies the geographic location of the listings and the web sourcewhenever applicable. In addition, the database identifies variousaspects of the form that are needed for automatic querying, including:which fields in the form are required in order to query through it;which properties of the objects are provided by the answers to thequeries; and how the fields in the form map to fields of the database.

Content creation—various embodiments of the present inventionautomatically find sources for the search engine and automatically guesshow to place them in the database. For each web form, a number of itemsare predicted, including: the most likely classes of the objectsobtained by the form; the nature of the source; the location of thecontents; and the mappings of the fields of the web form to propertiesof the objects. This enables a human annotator to later review theguesses made and correct them if necessary. In various embodiments, thetool includes one or more of the modules: (a) a module for locatingforms in an HTML page, (b) a module for extracting the names of thefields in the form from the HTML, (c) a module for predicting the classof a web source, (d) a module for predicting the class of web formswithin a web source, (e) a module for predicting the location associatedwith a web source and form, (f) a module for predicting the mapping ofthe web-form fields, (g) a module for predicting the output propertiesof a web form, and (h) a module for predicting the required fields of aform.

Querying and ranking—Given an input keyword query, the above-describedengine generally finds the web pages with the most relevant web formsand ranks them appropriately. In some cases, an answer to a query is aranked set of forms, each of which can be consulted further to obtainrelevant data. In other cases, the engine fills out the form anddisplays the answers obtained from filling the form. In variousembodiments, a user may see a partially filled form and thereforeexpedite the query answering process (or correct the inputs to the form,if necessary). In various embodiments of the present invention, thequery-answering process may involve two components: (1) a queryanalyzer; and (2) a ranking module.

The query analyzer analyzes the query to map it to the terms of theontology. The following predictions may be made by the query analyzer: aclass (or set of classes) in the ontology that the query is most likelyconcerned with, the set of properties of that class that are mentionedin the query, constraints in the query (e.g., a person's name, carmodel), and a location that the query may be referring to.

The ranking module orders web pages in the database by the relevance oftheir web forms to the user query. In doing so, the ranking moduleconsiders one or more the following factors: (a) the class in theontology that the query and the web forms map to, (b) the propertiesmentioned in the query, (c) proximity to the location mentioned in thequery and associated with the web source, (d) importance (page rank) ofthe web source, (e) keyword relevance between the web source and thequery, (f) related classes in the ontology, and (g) classes that can beinferred from the keywords in the results to the query.

Querying through forms—The above-described engine lets user querythrough web forms by deriving from the user's query the input values forfields in the forms. To do so, the engine considers: the set of requiredfields in the form, the mapping between the form fields and the ontologyproperties, and set of other items. These other items can include: (a) amapping from values in the query string to specific instance values ofontology properties, (b) a mapping from values in the query string tovalues mentioned in selection menus in the form, (c) translations offormats from the query into those in the form, and/or (d) a choice ofradio buttons or checkboxes in the form to pose a precise query to theform's server.

The foregoing descriptions of embodiments of the present invention havebeen presented only for purposes of illustration and description. Theyare not intended to be exhaustive or to limit the present invention tothe forms disclosed. Accordingly, many modifications and variations willbe apparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the present invention. The scope ofthe present invention is defined by the appended claims.

1. A method for searching through content which is accessible through aweb-based form, the method comprising, in a computer system, performingthe operations of: receiving a query containing keywords; analyzing thequery to create a structured query, the analyzing comprising: predictinga class for the query based at least on the keywords in the query;mapping the keywords in the query to properties of the predicted class;and generating a structured query based on the mapping; performing alookup based on the structured query in a database containing an entryfor each of a plurality of web-based forms; ranking web-based formsreturned by the lookup, wherein ranking the web-based forms comprisesdetermining one or more scores for each web-based form based onproperties of a web page in which the web-based form is located, whereindetermining the one or more scores comprises determining a form scorethat reflects an ability of the web-based form to answer the query by:determining inputs and outputs for a first web-based form based on thepredicted class for the query; determining inputs and outputs for asecond web-based form in the database; and computing the form score forthe first web-based form using the inputs and outputs for the firstweb-based form and the inputs and outputs for the second web-based form;and facilitating a search of content that is accessible through theweb-based forms using the rankings.
 2. The method of claim 1, whereinfacilitating the search of content that is accessible through theweb-based forms using the rankings comprises searching one or more formsof interest, wherein the forms of interest are ranked in order accordingto a relevance of each web-based form to the query.
 3. The method ofclaim 2, wherein searching the one or more forms of interest involvespresenting a ranked form to a user through a one-box displayed within auser interface.
 4. The method of claim 2, wherein searching the one ormore forms of interest comprises: presenting a user with a query-throughlink to a form of interest; and in response to user selection of thequery-through link, automatically submitting a query corresponding tothe query-through-link to the form of interest.
 5. The method of claim4, wherein presenting the user with the query-through link to the formof interest comprises: mapping keywords from the query to input fieldsin the form of interest; constructing a query-through link based on themappings, wherein the query-through link comprises an invocation stringto be submitted to the form of interest; and presenting thequery-through link to the user.
 6. The method of claim 1, whereindetermining the one or more scores for each web-based form furthercomprises determining one or more of the following: an approximatepage-rank score reflecting a count of incoming links to a web pageassociated with the web-based form; a keyword score reflecting therelevance of text associated with the web page associated with theweb-based form; an ontology score reflecting the relevance of theselected search-ontology class for the query to the web page associatedwith the form; and a location score reflecting the distance from arelevant location for the web page associated with the web-based form tolocations detected in the query.
 7. The method of claim 1, wherein thesecond web-based form (f) is associated with a page (p), and whereincomputing the form score using the inputs (Q_(I)) and outputs (Q_(O))for the first web-based form and the inputs (I_(f)) and outputs (O_(f))for f comprises computing a form score (FS(p)) for the page p based on aform score (FS(f)) for each of the web-based forms f:${{{FS}(p)} = {\max\limits_{f \in p}\;{{FS}(f)}}},$ wherein${{FS}(f)} = {\frac{{I_{f}\bigcap Q_{I}}}{{I_{f}\bigcup Q_{I}}} \cdot {\frac{O_{f}}{Q_{O}}.}}$8. The method of claim 1, wherein the method further comprisesdetermining a combined score for ranking a given web-based form bycomputing a linear combination of the one or more scores for the givenweb-based form.
 9. The method of claim 8, wherein computing the linearcombination comprises: assigning a weight to at least one of the scores,wherein a value for the weight is determined based on a type of score towhich the weight is assigned.
 10. The method of claim 1, whereinpredicting the class for the query comprises performing at least one of:a word-based prediction, wherein the word-based prediction comprisespredicting one or more classes that are likely to generate the keywordsin the query; a property-based prediction, wherein the property-basedprediction comprises predicting one or more classes that are likely togenerate one or more recognized property values in the user query; afeedback-based prediction, wherein the feedback-based predictioncomprises predicting a class based on a result of a keyword query usingthe keywords in the query; or a location detection, wherein locationdetection comprises predicting a class based on keywords in the querythat are determined to be a name of a location.
 11. A computer-readablestorage device storing instructions that when executed by a computercause the computer to perform a method for searching through contentwhich is accessible through a web-based form, the method comprising:receiving a query containing keywords; analyzing the query to create astructured query, the analyzing comprising: predicting a class for thequery based at least on the keywords in the query; mapping the keywordsin the query to properties of the predicted class; and generating astructured query based on the mapping; performing a lookup based on thestructured query in a database containing an entry for each of aplurality of web-based forms; ranking web-based forms returned by thelookup, wherein ranking the web-based forms comprises determining one ormore scores for each web-based form based on properties of a web page inwhich the web-based form is located, wherein determining the one or morescores comprises determining a form score that reflects an ability ofthe web-based form to answer the query by: determining inputs andoutputs for a first web-based form based on the predicted class for thequery; determining inputs and outputs for a second web-based form in thedatabase; and computing the form score for the first web-based formusing the inputs and outputs for the first web-based form and the inputsand outputs for the second web-based form; and facilitating a search ofcontent that is accessible through the web-based forms using therankings.
 12. The computer-readable storage device of claim 11, whereinfacilitating the search of content that is accessible through theweb-based forms using the rankings comprises searching one or more formsof interest, wherein the forms of interest are ranked in order accordingto a relevance of each web-based form to the query.
 13. Thecomputer-readable storage device of claim 12, wherein searching the oneor more forms of interest comprises presenting a ranked form to a userthrough a one-box displayed within a user interface.
 14. Thecomputer-readable storage device of claim 12, wherein searching the oneor more forms of interest comprises: presenting a user with aquery-through link to a form of interest; and in response to userselection of the query-through link, automatically submitting a querycorresponding to the query-through-link to the form of interest.
 15. Thecomputer-readable storage device of claim 14, wherein presenting theuser with the query-through link to the form of interest comprises:mapping keywords from the query to input fields in the form of interest;constructing a query-through link based on the mappings, wherein thequery-through link comprises an invocation string to be submitted to theform of interest; and presenting the query-through link to the user. 16.The computer-readable storage device of claim 11, wherein determiningthe one or more scores for each web-based form further comprisesdetermining one or more of the following: an approximate page-rank scorereflecting a count of incoming links to a web page associated withweb-based form; a keyword score reflecting the relevance of textassociated with the web page associated with the web-based form; anontology score reflecting the relevance of the selected search-ontologyclass for the query to the web page associated with the form; and alocation score reflecting the distance from a relevant location for theweb page associated with the web-based form to locations detected in thequery.
 17. An apparatus that searches through content which isaccessible through a web-based form, comprising: a processor; a memorycoupled to the processor; a receiving mechanism coupled to theprocessor, wherein the receiving mechanism is configured to receive aquery containing keywords; an analysis mechanism coupled to thereceiving mechanism, wherein the analysis mechanism is configured toanalyze the query to create a structured query, the analyzingcomprising: predicting a class for the query based at least on thekeywords in the query; mapping the keywords in the query to propertiesof the predicted class; and generating a structured query based on themapping; a lookup mechanism coupled to the analysis mechanism, whereinthe lookup mechanism is configured to perform a lookup based on thestructured query in a database containing an entry for each of aplurality of web-based forms; a ranking mechanism coupled to the lookupmechanism, wherein the ranking mechanism is configured to rank formsreturned by the lookup, and wherein when ranking the forms returned bythe lookup, the ranking mechanism determines one or more scores for eachweb-based form based on properties of a web page in which the web-basedform is located, wherein determining the one or more scores comprisesdetermining a form score that reflects an ability of the web-based formto answer the query by: determining inputs and outputs for a firstweb-based form based on the predicted class for the query; determininginputs and outputs for a second web-based form in the database; andcomputing the form score for the first web-based form using the inputsand outputs for the first web-based form and the inputs and outputs forthe second web-based form; and a searching mechanism coupled to theranking mechanism, wherein the searching mechanism is configured tofacilitate a search of content that is accessible through the web-basedforms using the rankings.
 18. The apparatus of claim 17, wherein whenfacilitating the search of content that is accessible through theweb-based forms using the rankings, the searching mechanism isconfigured to search one or more forms of interest, wherein the forms ofinterest are ranked in order according to a relevance of each web-basedform to the query.
 19. The apparatus of claim 18, wherein whilesearching the one or more forms of interest, the searching mechanism isconfigured to present a ranked form to a user through a one-boxdisplayed within a user interface.
 20. A system for searching throughcontent which is accessible through a web-based form, comprising one ormore computers configured to perform operations comprising: receiving aquery containing keywords; analyzing the query to create a structuredquery, the analyzing comprising: predicting a class for the query basedat least on the keywords in the query; mapping the keywords in the queryto properties of the predicted class; and generating a structured querybased on the mapping; performing a lookup based on the structured queryin a database containing an entry for each of a plurality of web-basedforms; ranking web-based forms returned by the lookup, wherein rankingthe web-based forms comprises determining one or more scores for eachweb-based form based on properties of a web page in which the web-basedform is located, wherein determining the one or more scores comprisesdetermining a form score that reflects an ability of the web-based formto answer the query by: determining inputs and outputs for a firstweb-based form based on the predicted class for the query; determininginputs and outputs for a second web-based form in the database; andcomputing the form score for the first web-based form using the inputsand outputs for the first web-based form and the inputs and outputs forthe second web-based form; and facilitating a search of content that isaccessible through the web-based forms using the rankings.
 21. Thesystem of claim 20, wherein facilitating the search of content that isaccessible through the web-based forms using the rankings comprisessearching one or more forms of interest, wherein each form of interesthas a rank that is higher than the rank for one or more other web-basedforms returned by the lookup.
 22. The system of claim 21, whereinsearching the one or more forms of interest comprises presenting aranked form to a user through a one-box displayed within a userinterface.
 23. The system of claim 21, wherein searching the one or moreforms of interest comprises: presenting a user with a query-through linkto a form of interest; and in response to user selection of thequery-through link, automatically submitting a query corresponding tothe query-through-link to the form of interest.
 24. The system of claim23, wherein presenting the user with the query-through link to the formof interest comprises: mapping keywords from the query to input fieldsin the form of interest; constructing a query-through link based on themappings, wherein the query-through link comprises an invocation stringto be submitted to the form of interest; and presenting thequery-through link to the user.
 25. The system of claim 20, whereindetermining the one or more scores for each web-based form comprisesdetermining one or more of the following: an approximate page-rank scorereflecting a count of incoming links to a web page associated withweb-based form; a keyword score reflecting the relevance of textassociated with the web page associated with the web-based form; anontology score reflecting the relevance of the selected search-ontologyclass for the query to the web page associated with the form; and alocation score reflecting the distance from a relevant location for theweb page associated with the web-based form to locations detected in thequery.